Each allowed_domains entry can now carry its own backend {host, port}.
That lets one proxy on port 25565 serve multiple MC servers, picking
the upstream from the domain the client typed.
- proxy/main.py: ProxyState.backend_for(domain) → tuple|None,
honors per-domain backend first, falls back to top-level backend.
handle_client uses backend_for(); blocked / disabled domains
return None (and still get a Login Disconnect on join attempts).
- api/routes/{config,domains}.py: DomainBackend model + optional
backend field on create/patch. PATCH supports clear_backend=true
to drop a per-domain override and revert to default.
- frontend/Domains.jsx: full rewrite — new-domain form has host/port
inputs, table shows each row's effective backend, inline edit +
reset button per row.
- frontend/Settings.jsx: backend section relabeled "기본 백엔드 (fallback)"
- README updated with multi-server example config.
Previously a blocked join just dropped the socket, so the MC client
showed 'Internal Exception: SocketException: Connection reset'.
Now when next_state=2 (login), the proxy sends a proper Login
Disconnect (0x00) packet containing a JSON chat component, and the
client displays the message on its disconnect screen.
- block_message added to config (default Korean message); editable
in Settings UI as a textarea
- build_login_disconnect() encodes (varint length)+(0x00)+(JSON str)
- Status/ping (next_state=1) still silently dropped so the proxy
presence is not announced to scanners
- Backward-compat: load_config() backfills block_message on old files
